bad ventilation for gas furnace

Old 03-20-01, 06:00 AM
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I recently installed a 70,000 btu nat. gas furnace in my home. It worked fine for a month or so, then the steam or gasses that should flow out the top of the vent began blowing right out the back of the furnace inside the house.There is a sensor in the back reading the gasses and shutting off the pilot and everything.I can re-light it but it keeps shutting down .The section of vent that runs through the wall is ice cold and it feels like a strong backdraft of cold air. I thought I fixed it when I sealed the elbow where the vent turns to go up along the wall outside, but now it is doing it again.
Old 03-20-01, 08:34 PM
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Post Restricted Exhaust Vent

Hi: steeler74

The problem discription sounds like there are several possibilities.

The vent to the roof is either restricted or too small.
This may be do to a defective vent cap, restricted, damaged or incorrectly installed cap.

If the prior furnace was a smaller BTU unit, the existing vent pipe may be too small. The existing vent piping may not be installed correctly no the new unit or incompatible with the unit. Especially if the new unit has a forced drafted vent system.

The angle or angles and or the number of angles of the pipe could be the problem. The downdraft diverter on the heating unit could be installed incorrectly or it's defective.

The vent piping may not be the correct height above the roof line. Lots of possibilities can be incorrect.

The main point is the furnace isn't venting correctly. If all the above conditions appear correct, you'll need to have a heating agent check it. Fumes coming back down from the vent pipe can be hazardous.

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